1. Field of Invention
The field of the currently claimed embodiments of this invention relates to systems and methods for separating metallic and nonmetallic particles in a mixed-particle suspension.
2. Discussion of Related Art
Since the success of integrated silicon technology of the metal oxide semiconductor field-effect transistor (MOSFET), the ability to scale down the dimensions of the device has been the key to improving speed and energy efficiency1-2. However, the industry generally expects that fundamental material barriers will limit the size reduction of current nanoscale MOSFET devices and that this road block to continuing advancement will arrive within a decade as predicted by Moore's law2. In order to overcome these barriers, new materials are needed to solve the scalability problems of future silicon devices. Among these new silicon substitute materials, single-walled carbon nanotubes (SWCNTs) have become excellent candidates as building blocks for future nanoscale electronics due to their small size and unique electrical properties. SWCNTs have been actively pursued as electronic materials and silicon device substitutes since Ijima and Bethune independently discovered them in 19931-4. However, current SWCNT production techniques generate a mixture of two types of nanotubes with divergent electrical behaviors. Some of the nanotubes act as metallic materials, while others display semiconducting properties. This random mixture has complicated the realization of functional carbon nanotube-based nanoelectronics3,5-6. SWCNTs can be considered to be a single rolled-up graphene sheet7. Variability during production of SWCNTs leads to tubes of different diameter and atomic configuration relative to the tube axis (degree of chirality)2,7. These structural variations dictate the electronic properties of SWCNTs and can result in metallic or semiconducting nanotubes.
Current commercial processes for SWCNT separation require ultra-centrifugation and require large amounts of time, energy, and equipment to run. Significant research has been conducted on using dielectrophoresis (DEP) as an alternative means of purification, but the state of the art techniques demonstrated by to date are significantly handicapped. Conventional DEP separation devices and techniques are static systems and only pull metallic nanotubes onto the device surface, leaving semiconducting and some metallic tubes in suspension. These devices only handle small fixed-volumes of mixed SWCNT and the working areas of the devices are cluttered by nanotubes after each pass. Only the metallic nanotubes deposited at the electrode can be extracted with high purity. The remaining suspension is still a mixture and removing this excess volume can result in contamination of the high purity surface. There thus remains a need for improved systems and methods for separating metallic and nonmetallic particles in a mixed-particle suspension.